A personal watercraft is a relatively small buoyant vessel with a hull which provides a platform on which its rider stands or sits during operation. It may but usually does not, carry more than one--at most two or three. It is a sporting vessel not intended for long voyages, or primarily for passenger transportation from place to place. Most frequently it is a recreational vehicle. It includes handle means for steadying the rider and for guiding the watercraft. It supports a motor and an impeller. The motor drives the impeller, which receives a supply of water and discharges it rearwardly as a jet to drive the watercraft along the surface of the water. The intake port to the impeller is located in the bottom of the watercraft, and the nozzle discharges into the atmosphere.
If personal watercraft were operated only at lesser velocities in smooth water, and in waters without debris, it would be adequate and permissible for the intake port simply to open directly into the water. The intake port would be beneath the water, and water would simply be drawn into the impeller system, without complications. The bottom of the hull would be sufficiently underwater to assure a source of water for the impeller.
However, this type of operation is almost precisely what a watercraft owner does not want it to do. It is not long after he buys one until the owner strives to achieve high velocities in rough water, and even in the surf. Championship riders actually "shred" the waves, driving up their slopes, into the air, and down again to fall into turbulent water. They drive these vessels along the face of a wave, often through the "tube" and even into very shallow water where there may be considerable debris and exposure to abrasion.
For this reason, personal watercraft are generally provided on their bottom with a plate commonly called a "ride plate". It functions to protect a major portion of the hull from abrasion, and also provides a chamber between it and the bottom of the hull from which the impeller draws water rather than from the body of water without an intervening barrier. Because the watercraft tends to ride up out of the water at higher velocities, frequently only the ride plate itself is submerged. It must therefore function both as part of a water supply acting as a scoop and also as a means for stabilizing the movement of the watercraft in the water.
Ahead of the ride plate, it is customary to provide an intake grate. As its name implies it is intended to act as an intake grate to pass water to the intake chamber, and thence through the impeller and pump, and hopefully to exclude substantial debris.
To attain the very substantial velocities contemplated by riders of personal watercraft, it is evident that neither the ride plate nor the intake grate should constitute a substantial impediment to the requisite flow of water. This is a difficult task, especially because the intake grate is provided for the purpose of exclusion of material. Still, material which enters into the chamber between the bottom of the watercraft and the top of the ride plate should be kept as free as possible from debris lest the debris be drawn into the impeller. Screens cannot effectively be used, because they can clog up.
A ride plate presents yet another challenge, especially when installed on watercraft which will be used for challenging maneuvers. By the term "challenging" is meant high velocity movement in circumstances where close control of the direction and orientation of the watercraft is important. Examples of these circumstances are racing, sharp turns, loops, jumps, and rides in unusual circumstances such as up and over, or along, the face of a wave. In those circumstances, skewing, side slip, and other variations from a true directed movement can be very risky to the rider and to the watercraft.
In fact, certain adverse conditions are well-known to exist and to spoil the accuracy and response of the movement of the conventional watercraft. One is commonly called "cavitation". Because ride plates rapidly pass through a stream during operation, they exert the classical responses of a plate in a rapidly moving fluid stream. The plate lifts with the craft, even assisting the lift, and the reaction with the water, especially as to sidewise or skew motion, is less responsive. This can lead to side skids, and can complicate an intended banking of the craft.
It is an object of this invention to provide a ride plate that includes an intake grate which has foil characteristics that enable passage through the water with minimal resistance, with good exclusion of debris, and protection of the vessel in the event of contact with a relatively unyielding body such as a sandy beach, or even a rocky area.
It is a further object of the invention to provide the ride plate with a bottom surface which is gently "vee-ed" to provide for lateral stability, which has cupped edges effective for stabilizing purposes in high speed turning maneuvers, and downwardly projecting fins which assist in high speed turns and in deep "carving" turns.